Page:Territory in Bird Life by Henry Eliot Howard (London, John Murray edition).djvu/336

268 ground already occupied, and, until reproduction is completed, asserts its individuality and exercises dominion over its territory. What, then, is the prospective value, biologically considered, of the changing interest that A displays in B, and to what will such changes lead? These are the questions to which we will now direct inquiry.

The annual life-history of a bird is in broad outline conditioned by two powerful and at first sight opposing impulses—the one to live in society, the other to live solitary. But, manifestly, a bird cannot be governed by opposing impulses. It has but one character, within which, according to the season and the circumstances, different impulses predominate. But these impulses, no matter how different they may appear to be, have their respective parts to play in furthering the life of the individual. Hence they cannot oppose, though they may conflict, if the resultant behaviour contributes towards survival.

The majority of birds live to-day in constant danger from predatory species, and that this danger was still greater in bygone ages there can be but little doubt. A curious mode of behaviour of the Curlew, Whimbrel, and Godwit demonstrates this, for it must be the outcome of the necessity for constant watchfulness. Whilst resting with its head turned back and its beak buried in the feathers of the mantle, the bird constantly moves the axis of its body, so that an observer, if placed in a direct line